Creep, recrystallisation and anelasticity of hcp-metals

具有六方密包（hcp）结构的金属和合金（如镁、锌、钴）是重要的工业材料。六方钛和锆合金是航空航天和核能领域的关键材料。蠕变特性是它们成功的关键，同时也是限制因素。铁在~11GPa以上采用hcp结构，维持地球磁场的能量来自液态铁的外核结晶成六方密包（hcp）铁。地球内核的性质主要是从地震波穿过地核时的速度和衰减来推断的。稳定hcp铁（>2 GPa）和地球内核（>50 GPa, bbb5500 K）所需的极端条件意味着对其蠕变行为或对循环变形的响应知之甚少。在这个项目中，学生将研究高温高压金属和合金蠕变和小振幅循环（正弦）变形的实验系统，以及高温下的扩散和退火测试。初步实验将在1大气压高温蠕变装置上进行。来自测试的力学数据将与扫描电子显微镜（SEM）和电子探针分析（EPMA）相结合，以了解实验样品中发生的晶体学和材料过程。这项工作将继续进行到其他样品和更高的压力。金属和合金对小振幅循环载荷的响应对于理解地球内核和材料成型和工业过程都很重要。

Metals and alloys with the hexagonal close pack (hcp) structure (e.g. magnesium, zinc, cobalt) are important industrial materials. Hexagonal titanium and zirconium alloys are key materials in the aerospace and nuclear energy sector. Creep properties are key to their success as well as often being the limiting factor. Iron adopts the hcp structure above ~11GPa and the energy to sustain the Earth's magnetic field comes from crystallization of the liquid iron outer-core into hexagonal close pack (hcp)-iron. The properties of the Earth's inner-core are inferred primarily from the speed and attenuation of cyclic, seismic waves as they transverse the core. The extreme conditions needed to stabilize hcp iron (>12 GPa) and those of the Earth's inner core (>250 GPa, >5500 K) mean that comparatively little is known about its creep behavior or its response to cyclic deformation. In this project the student is studying the experimental systematics of hcp metals and alloys to both creep and small amplitude cyclic (sinusoidal) deformation as well as diffusion and annealing tests at elevated temperatures. Initial experiments will be conducted on magnesium using a 1 atmosphere high temperature creep apparatus. The mechanical data from the tests will be combined with scanning electron microscope (SEM) and electron microprobe analysis (EPMA), to understand the crystallographic and material processes that occur in their experimental samples. The work will progress to other samples and higher pressures. The response of metals and alloys to small amplitude cyclic loading is important for both understanding of the Earth's inner-core and material forming and industrial processes.